The field of the invention is input/output interface racks for control systems such as programmable controllers, process controls and numerical controls, and particularly, means for mounting a number of input and output interface circuits for such a control system and connecting them to the machine being controlled.
In electrical control systems such as solid state controllers, numerical controls, programmable controllers and process controls, the circuits which interface the system to the machine being controlled are typically mounted on printed circuit boards which are arranged alongside one another and are interconnected by a wiring harness or a "mother board". The electrical connection of such interface circuits to the machine being controlled is made by the user and it may involve the connection of hundreds or even thousands of wires to terminals on the interface circuit boards.
In I/O interface racks such as those disclosed in U.S. Pat. Nos. 3,992,654 and 3,942,077, the wire terminals on each interface circuit board are disposed along its front edge where they are readily accessible to maintenance personnel. In most applications there wire terminals are not connected directly to the controlled machine, but instead, are connected thereto through a terminal block which is mounted within the same enclosure as the I/O interface rack. Terminal blocks such as that disclosed in U.S. Pat. No. 3,236,975 are often employed for this purpose because they are suitable for use in industrial environments. Such terminal blocks are rugged and have been employed for years in industry when "field wiring" is necessary. In prior I/O interface racks it becomes necessary to hand wire the terminals on the interface circuit boards to the heavy duty wire terminals in addition to hand wiring those terminals to the devices on the controlled machine. This additional hand wiring adds considerably to the overall cost of the control system.